1. Technical Field
The present invention relates to a reverse driving signal for a vehicle, such as a tractor-trailer. In particular, the present invention relates to a reverse driving signal that can be used for, for example, to activate a back-up light or back-up alarm or any other accessory that is to be turned on or off during or before reverse driving of the vehicle.
2. Description of the Prior Art
Backing a vehicle can potentially be hazardous especially when backing with a trailer and when visibility behind the trailer is poor. It is known to provide a back-up light or back-up alarm that is activated while backing up, to warn pedestrians to be alert when crossing behind the trailer.
It is known to generate a reverse driving signal in either the tractor or the trailer. In the tractor, the reverse driving signal is typically generated by a simple electrical switch that is closed when the transmission is put in reverse. A tractor generated reverse driving signal requires a hard wire connection to the trailer to transmit the reverse driving signal to the back end of the trailer where the back-up light or alarm is located. The hard wire for transmitting the reverse driving signal to the trailer may alternatively be part of a second connector between the tractor and trailer, or the signal may alternatively be transmitted via a communication link, e.g., Power Line Communication (PLC) over an existing wire in the seven-conductor electrical connector jumper cable (according to SAE J 560) as is currently used in some new tractor/trailers. A second connector is expensive and must be installed both on the tractor and on the trailer. That limits the flexibility of use a trailer with different tractors and of a tractor with different trailers. Therefore a second connector is used only in a very low number of special tractor/trailer combinations. To transmit the tractor generated reverse driving signal to the trailer via a communication link requires also the availability of such a communication link in both tractor and trailer. Many trailers built before Mar. 1, 2001 do not have PLC and will be in use yet for many more years after that date. Therefore a communication link is also a limited option.
A trailer generated reverse driving signal is typically provided by an electronic sensor, e.g., a Hall-effect sensor, that is associated with a rotatable road wheel of the trailer. This type of sensor is relatively expensive, requires a protected and clean environment, and can detect reverse driving only when the trailer is in motion.